The present invention relates generally to optoelectronic devices and more specifically to environmentally sensitive optoelectronic devices. These devices include organic optoelectronic devices such as organic light emitting diodes (OLED) be it either small molecules or polymer type, organic photovoltaic devices, organic thin film transistors, and organic electrochromic displays, electrophoretic inks, solar devices, and LCD's in general (including applications for watches, cell phones etc.).
Many such optoelectronic devices are known in the art. However, specifically organic optoelectronic devices such as OLEDs have not yet made their predicted significant economic and technical breakthrough. This is partially due to the fact that the organic structures and the cathodes need to be heavily protected from the environment, specifically from oxygen, from water and from water vapor.
Currently, many optoelectronic devices (such as LCD and OLED displays) are manufactured by depositing thin film structures on a glass substrate, which has excellent optical properties and which is also an excellent environmental barrier. Most organic optoelectronic devices today are also manufactured on glass substrates and are encapsulated in glass (or in metallic-) structures. By its brittle nature however, glass does not provide flexibility and light weight. By using thin, flexible polymeric substrates for OLEDs in particular—which is known in the art—and by thin encapsulation layers for the device, a high degree of flexibility and lightweight shall be obtained. However, the following problems arise simultaneously:
Thin polymeric substrates and organic structures have a diffusion coefficient for oxygen and for water, which is far too high to protect the enclosed structures from degradation.
Thin polymeric substrates and organic structures are susceptible to degradation, deformation and building up of thermally induced stresses when the functional layers are deposited due to the process temperature created intentionally or unintentionally during the deposition.
For illustration, FIG. 1 shows the typical build up for an organic optoelectronic device on an organic substrate: in order to protect the device (here an OLED pixel with its electrodes) from the environment, a barrier layer between the polymeric substrate and the device, and an encapsulation layer covering the whole device are necessary. FIG. 1 shows a cross section of an OLED device, with an flexible substrate 1, a barrier layer 2, a transparent conductive oxide (TCO) layer 3, OLED layer(s) 4 (organic), cathode 5 and encapsulation layer 6
Both, the organic layers 4 and also the metallic cathode 5 need to be protected from oxygen and vapor diffusion, the market requires that the device to be light weight and flexible, the functional layers to be transparent for light of the desired wavelength, the device to be easily manufacturable and the functional layers to have excellent mechanical properties. Additionally, the encapsulation layer 6 needs to offer some mechanical and chemical stability, must seal off the device hermetically and must closely fill the complex top structure of the device during application of the film (step coverage).